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Патент USA US3084303

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April 2» 1963
J. MUNUsHlAN ETAL
3,084,293
MICROWAVE AMPLIFIER
Filed April 1, 1959
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MICROWAVE AMPLIFIER
Filed April 1, 1959
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J. MUNUSHIAN ETAL
3,084,293
MICROWAVE AMPLIFIER
Filed April l, 1959
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April 2, >1963
J. MuNUsHlAN EI-AL
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MICROWAVE AMPLIFIER
Filed April l, 1959
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4 Sheets-Sheet 4
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United States Patent O ” ICC
1
3,084,293
MECRÜWAVE AMPHFÍER
.iaclt Mnnushian, Pasadena, and .lack Kläger, Los Angeles,
Caiif., assigncrs to Hughes Aircraft Company, Culver
City, Caiif., a corporation of Delaware
Filed Apr. 1, 1959, Ser. No. 803,425
3 Claims. (Cl. S30-43)
This invention relates to electronic amplifiers, and par
ticularly to microwave amplifiers having large dynamic
3,084,293
Patented Apr. 2, 1963
2
A further object of this invention is to provide systems
for appreciably increasing the dynamic range of existing
microwave amplifiers.
Another object of this invention is to provide improved
microwave amplifiers having signal compression capabili
ties.
A further object of this invention is to provide improved
logarithmic amplifiers which operate in the microwave
region and provide a marked increase in dynamic range
over a wide bandwidth.
’
ranges, especially those which are capable of synthesizing 10
Yet another object of this invention «is to provide travel
desired signal characteristics, such as logarithmic or limit
ing-wave devices which are capable of synthesizing se
ing responses.
lected response characteristics giving increased dynamic
The general problem of increasing the Versatility of am
range.
plilication equipment in electronic systems is well known.
Still another object of this invention is to provide am
15
For example, it is recognized that if the dynamic range
plifying devices which operate from a microwave RF
of a receiver can be increased by suitable amplification
signal to provide an output of desired characteristics.
devices, it is possible to detect small signals more reliably
Yet another object of this invention is to provide a
against a noise background. An increase in dynamic
high gain and wide bandwidth microwave amplifier capa
range also decreases the tendency of a receiver to saturate
ble of providing logarithmic amplification or limiting
when large signals are being received. This is especially 20 action.
important if i-t is desired to receive small signals against
A further object of this invention is to provide micro
a background of large interfering signals. Thus, an in
wave amplifiers of improved dynamic range which can
crease in the dynamic range of an amplifier can provide
immediate improvements in the systems in which it is 25
used.
provide RF to RF, RF to IF or RF to video operation.
These and other objects of the present invention are
achieved by an arrangement utilizing a successive-signal
removal technique with traveling-wave devices. In one
form of the invention, an adding helix may be positioned
dynamic range is accompanied by a precise calibration
adjacent to the helix of a traveling-wave tube. This form
of the signals in accordance with a known characteristic, 30 of the device constitutes RF to RF operation of the ampli
At the same time, however, it is also desirable to be
able to synthesize certain responses. If the increase in
a number of operative advantages may be derived and
fier while simultaneously providing a `desired total re
system requirements may be considerably simplified.
sponse such as, for example, extended dynamic range 0f
rl`hus, if the amplifier can have a logarithmic response, the
a logarithmic or 0f la flat limiting nature.
increase in dynamic range is accompanied by the ability
helix
directly to provide a visual representation or recorded 35 helix
output on a logarithmic scale. Similarly, a limiting re
wave
sponse at a selected level is extremely useful in many
each
The adding
is of like configuration and characteristics to the
of the traveling-wave tube. A number of micro
couplers are used along the length of the two helices,
coupling arrangement providing an exchange of
systems.
While logarithmic amplifiers and limiters, for example,
energy from a region of the principal helix to an associated
tively make use 4of amplifiers which convert from a micro
wave signal to a video signal with a logarithmic character
sections may be so designed as to synthesize the desired
region of the adder helix. The arrangement is such that
are well known at the lower frequencies, it is desirable 40 the continually increasing energy in the traveling Wave
in many instances to provide increased dynamic range in
of the traveling-wave tube is successively coupled out and
the microwave region of the spectrum. Many uses can be
onto the adder helix, so as to generate a corresponding
described for devices which convert, with some amplifica
traveling wave.
tion and a synthesized response characteristic, from RF
A uniform attenuating coating on the traveling-wave
Ito RF, from RF to IF, or from RF to video. Microwave 45 tube may be used to establish uniformity between the
preamplifiers can appreciably increase the -sensitivity of
sections and to reduce backward waves.
a receiver. Many instrumentation applications can effec
The saturation characteristics of the successive tube
total response. Although the output of each coupling
istie. High resolution radar systems could be appreciably 50 uni-t -saturates at a different level of input signal, the signal
improved through the use of amplifiers operating from
contnibution from the unit .does not thereafter remain
RF to IF with concurrent increase in the dynamic range.
constan-t but decreases. The relationship between the
It would be highly advantageous when operating in
various coupling sections is, however, arranged to achieve
the microwave region to be able to use traveling-wave
the desired output characteristic. In addition, the ar
devices such as the traveling-wave tube and traveling 55 rangement between the input to the traveling-wave tube
wave versions of the maser and the parametric ampliñers.
These devices are well known as high gain amplifiers
pling is established to augment the system response at
having wide bandwidths, and are capable of extremely
very high linput signal levels.
low noise operation. Particular ones -of the enumerated
and the first coupling unit can be such that a direct cou
In another form of the RF to RF version of the in
devices are often especially suited for specific applications, 60 vention, the successively removed signals are combined
where gain, frequency, bandwidth or noise may be con
trolling factors. Consequently, if such devices can be
in proper relation through the use of coaxial line phase
employed so as to have additional capabilities, such as
combined to lform an adding arrangement, and which can
shifting, attenuating and coupling elements which are
an increased dynamic range, then important advantages
be adjusted to `synthesize the desired response.
can be realized. Receivers can be considerably simplified 65
According to other features of this invention, the suc
through the combination of preamplification and signal
cessive-signal-removal principle may be utilized with
compression functions. Such combinations of features
other signal yrecombination and addition arrangements.
are even more desirable, of course, if they can be achieved
In one form, there may be a successively tapped delay
with a lightweight, compact structure which does not
line, with the youtputs of each of the coupling points from
impose additional requirements on the system.
70 the traveling-wave tube being rectified and then applied
Therefore, an object of the present invention »is to pro
to a different point of the delay line. ln this arrange
vide improved microwave amplifiers.
ment, the values .of the elements within the delay line
3,084,293
4
andthe placement of' thercouplers may- be adjusted to
fashion. Along'the length ofthe traveling-wave tube 1i),
again provide the desired ampliñcation characteristics.
The rectifying elements are inserted in the’coupling >lines
»disposed a relatively uniformi resistive coating 17, such
between the traveling-wave -t'ube'- and the poin'tsï off the
delaylineso >as to providea videoV output' from the micro
wave signal. This form of device consti-tutes RF to'video
tion of absorbing microwave energy.
The traveling-wave .tube 1G is operated in a conven
on the outer surface of the’evacuated envelope 12, is
as aquadag or like material, which can perform the func
lator, the microwave signal on’ the traveling-wave -tube
may be converted ‘to a desired-intermediate frequency sig
nal» onI the' delay line. rlÈhis frequency conversion- is again
accompanied byf an increase lin the operating dynamic
tional fashion. A` stream of electrons is directed along
:the central axis of the 'tube 10» Ibetween the negatively
charged cathode in Áthe electron gun 1?:l and the collector
14 at «the other end. The electrons travel in energy in
terchange relationship with a traveling Wave propagated
along the helix l16, with the axial phase velocities of the
eleo'tïron’ stream» and the traveling wave being selected to
resultf in- amplification of the traveling wave due to the
exchange' of' energy between the streamv and' the traveling
range ofthe' traveling-waveY tube .andVK constitutes RF »to
wave.
operation.
'
Y
In» still anotherforrn of vthe invention, the rectifying'4
elements may be replaced by mixing elements which areV
each‘fed from a common local oscillator signalV source.
By properly adjusting the frequency of,v «the >local oscil-r
IF
operation.
Y
,
_
'
‘Vtlith‘l this arrangement,¿ input energy is provided from
an input circuit 2U (FIG. l) to an input coupler 23 through
,
` Although .the arrangements are illustrated as*~ utilizing
traveling-wave tubes, «they maybe constructed'W-ithequal
a coaxial lin'e 21, thev center conductor 22 of the coaxial
facility-«with other‘travelingfwave devices.V Thus they may
alsoV be employed-l with- t'raveliugLWa've masers or' para
line 21»»being wound» helically about ‘the envelope 12‘ of
metric amplitiers.
th'e- traveiingîwave tube 10 at a‘ point adjacent to the elec
-trïori goti-'13 end of the tubel lili The input coupler 23,
«i
therefore, -provides afmicrowave transmission 'line which
The novel feature'sof this invention', as' well -as-- the in~
-is'` eleetrornagnetically- coupled to the electron gun, or
vent-ion itself, may b_e better understood >by reference .to
lthe following description, taken' in connection; with the 25 inpu'tgend- of the principal helix 16. Energy provided
accompanying drawings, in which like reference numerals
refer -to like parts and in which:`
_
from the> input Vcircuit» is, therefore, launchedv onto the
principal helix` 14S-"froml the _input coupler 23.
'
Withfthis arrangement is also employed a separate
FIG; l is a simplified perspective view of an'RF to RF
version' of one form of microwave amplifier using'a suc~
adder helix 2_6 spaced apart Ifrom and substantially par'-Y
all'el tothe principal helix'` 1'6’; The adder helix 26 is
positioned within an elongated4 envelope 28 and has input
cessive-signal-removall technique inA accordance vwith the'
present'invent-ion;
-
Y
_
and output ends» corresponding Ito the like ends- of the
FIG: 2 is an enlarged side sectional view of the> ar
rangementof FIGi 1'; -
_
travelirig~wave-tube110~ A termination 29' is’formed by
attenuativeï-material positioned in the »output end of the
-
FIG. 3V is an enlarged> fragmentaryv view of- aY por-tion'
of the structure offFIGS: _lf'and 2';
_.
' ‘
35
FIG. 4 Yis a- `graph showing operating characteristics
which'canbe provided with the arrangement of FIGS. 1y
to- 3‘;A '
'
.
`figuration-and properties as‘the principaljhelix' 162 VSpeci->
tically,y the ’s_izel andï pitch of the adder helix 26 are made
approximately the-same as' those of the principal helix
_
FIG. 5'` ise'a’ representation’partlyjn-side elevation 'and
partly` irl-schematic form; of an RFjt'o video arrangement
of a-traveling-wave' amplifier inacc'ordance‘ with the suc->
cessive-signal-removal technique `ofthe present invention;
FIGS. _6‘and 7 are graphsv of _the'outpu-t signal as ay
function’ofithe input signalïfo'r the ” arrangement of' FIG1 5,l
when adjustment has* been"m'ade’ forlop'eration las? log-arithmic ampliher and a limiter, respectively;_
envelope 28 containingv the' adder helix 26.~ The adder
helix'26 is selec'tedïïto have'V substantially the same con
40
1'6g- so thati'the phase velocity versus frequencyA charac
teristic of the adder helix 26 is4 equal to that of the prin
cipal- heli-x16 in' thepresence of its attenuative iilm and
the electron‘lbeamfr Agaimthe means for supporting the
45
adder helixï 26 Within the surrounding envelope ¿§78` have
not been-'shown A microwave output coupler *3_0 consist
ingf- ofi a1 helicalimicrowavetransmission- line' 31 'term-inet»
' FIG:- 8" »is a' representation,~ partlyy in schematic and
inginït-he~` center' conductpr 353n of a coaxial line 32 cou
partly-in block diagram form; ofv 'antitli'ierarrangementv in
pledïto’anï outputçcircuitf‘SS" ('FI'G.> l) is-positioned at the
outputi end of they radder helix 26'for coupling off energy
ments to provide another form of RF to’RF operation; 50 propagated thereon:- The output circuit 35 is referred toy
asïprovidingï a “synthesized” output, in accordance with
FIG. 9 is a graph of the output signal as _a function
the»ni'a'nner'inv which desired responsesmay'be provided.
of the input signal for the `arrangement of FIG. 8; and`
The tub‘el-l'tlrmay- also havenv linear output` circuit 37,v
FIG. lO'is a schematic and block diagram representa
t-ion of another system in accordance with' the invention, 55 coupled Y_at the collector end 14 byV another output cou-plerV
'
showing the manner in which. RF" to IF operation is
laccordance with the invention; utilizing microwaveele-`
provided.
An .arrangement for providing an amplifier of veryv
great `dynamic range in the microwaye' regionA which
` With this arrangement thereis also employed a groupY
of l miciowave'ï ener-'gyI couplers '49, 41, 42, 43Y selectively'
positioned at spaced regions along the lengths of the prin-~
cipalï helix 1`6f'a'n‘d the adderl helix 26; Four of these
an RFto RF amplifier system. is illustrated'in FIGS. l, 2 60 couplers 40f to 43 areï shown and each consists'of one
helical coupler 46 to 49fresp`ectively Wound'about the ex
and 3, to -which reference isfnowrm’ade. The `arrange
terïior- ofthe envelopeL 12 which surrounds the principal
ment includes a traveling-wave tube 1t), including.' an
helix'1'6, one' helical'coupl'er S2 to 5_5'respectively woundj
evacuated envelope structure 12 (best seen in'FIG. 2)
about the‘envelopeïZSïcontainingj the adder helixA 26; and
having »the usual'form’of electron gun 13 and electronV
a’nlî interconnecting length-of transmission line 5S to 61
collector 14. A slow-‘Wave structure 16 extends alongjthe
respectively'. Each of the Vcouplers 46 to 49 or 52 to 55'
central length of >the traveling-wave tube 10 between the
is' in energy interchange relationship with-the associated
electron gun 13 and the «collector ends 14: The slow
helix'ló‘or >26,' as maybe seen in more detail in the frag
wave structure is here shown in the form of a helix 16,
linentaryïviewÀ of FIGLB. Any number of couplers can be
hereafter referred‘to Vas the principal-helix i16. Details of
the traveling-wave tube 10, including details of the gun 70 used consistent with space limitations, but it has been
foun’dïthat three or more are desirable for the synthesis"
structure ‘13 and focusing means (not‘shown), and details
off a smooth'- response characteristic. The Vvarious cou
of the manner in which the principal helix 16'is sup
utilizes the successive>signal-removal principle to _form
plers 46 to> 491er SZ'to’S'S*v may beembedded in hollow
ported, have been omitted for simplicity in the drawing.
cylinders’ 64 of a' plastic or other material which is sub
Thus, it will be understood «that focusing magnets’ or
electromagnets‘ (not'shown)' are employed in the' usual‘ 7 stantially transparent‘to" microwave energy.' Wheri‘ so
5
3,084,293
constructed, the couplers 40> to 43 may be constructed
individually and slid onto the associated envelopes =12 and
28 to the positions desired and with proper support and
spacing.
The arrangement constructed as shown in FIGS. 1, 2
and 3 provides amplification of applied input signals with
nals are recombined on the adder helix 26 is essentially
independent of frequency `and the device is substantially
`as broadband as the traveling-wave-tube l@ itself.
A number of details in the construction of this arrange
ment are to be noted, these details serving individually
and in combination to provide desirable features and to
enable the more ready synthesis of characteristic re
a response characteristic which can have a large dynamic
range, and which specifically can be a logarithmic char
sponses. The attenuating coating 17 upon the envelope
acteristic or a limiting characteristic if such is desired.
12 of `the traveling-wave tube 10 assists in establishing
The input circuit 20 provides the RF energy which it is l0 uniformity of the sections between the various couplers
desired to amplify, and this energy is launched onto the
‘to to 43. Further, Ithis attenuation material 17 reduces
principal helix 16 from the input coupler 23. As the
the reflective effects which result in backward waves be
traveling wave moves along the principal helix 16 from
ing propagated `along the helix 16, which waves would
the input to the output ends, it is amplified due to the
interaction between the electron stream and the traveling
wave.
The successive extraction or removal of signals
is accomplished by the separate energy couplers it()` to 43
disposed along the length of the principal helix 16. As
the energy reaches the coupling helix 46 closest to the
input end, for example, at least a portion of the energy is
coupled off to the coupler Alti, and transferred to the asso
increase the tendency to oscillate land which would also
reduce the gain of the system. The coupling ratio of
the various coupling sections 40 to 43 .is adjusted to be
less than unity, in order to insure that enengy is coupled
from the principal helix 16 and onto the adder helix 26
with a mininum lof coupling in a reverse direction. With
full unity coupling at the later helical coupling sections
53 to 55 on the adder helix 26, a portion of the recom
ciated coupling helix 52 about the adder helix 26, from
bined »traveling Wave might tend to enter these helical
whence it is launched onto the adder helix 26. The pro
couplers S3 to 55. Such energy would either be dissipated
portion of lthe traveling wave which is removed from the
at the termination of the coupler 53 -to 55 :or reflected b-aok
principal helix 16 and coupled onto the adder helix 26 25 to the principal helix 16. To keep these losses within
is determined in accordance with considerations given in
4limits which do not affect the synthesis of the desired re
more detail below. The couplers 40 to 43 are arranged,
sponse `the coupling ratio of the couplers 40 to 43 is here
as to the number of turns employed and their proximity
made less -than unity.
to the associated helices 16 and 2.6, to provide a selected
Further, the amount of the coupling of the individual
coupling proportion, which may be unity but is usually 30 couplers 46 to 49 on the principal helix 16 is decreased
somewhat less than unity.
between successive couplers 46 to 49* in the direction
Because of the like characteristics of the traveling waves
from the input end «toward the output end. This arrange
in the principal helix 16 and the adder helix 26, these
ment results in a monotonically increasing output signal
traveling waves have a like axial phase velocity. Energy
although further lmodifications may also be made when it
which is coupled off the principal helix 16 therefore estab
`is desired to synthesize centain yother responses. The
lishes a like traveling wave in the adder helix 26. After
reason for less coupling toward the output end is derived
the energy is extracted or removed, the traveling wave on
the principal helix 16 is again amplified by the time the
second coupler 41 is reached. Again, therefore, energy
is extracted and transferred to the adder helix 26 in the
saine manner as was accomplished at the first coupler 4f).
Because the axial phase velocities in the two helices 16,
26 are alike, and with the couplers ¿il to 43 having like
relative axial dispositions along the two helices 16 and
26, the energy extracted at the second coupler 41 from
the principal helix 16 is added to the traveling vwave along
the adder helix 26 in phase with the energy launched onto
the adder helix 26 from the first coupler 40. Conse
generally from the fact that with low level input signals
saturation occurs only toward the output end. The
maximum outputs of each of the couplers 46 to 49‘ are
approximately the same. Therefore, if the last coupler
49 along the path of the traveling wave has a high
amount of coupling, this constitutes a limitation upon the
total output signal, which cannot be made to increase
yabove the normal saturation point. Consequently, cou
pling is reduced toward the output end, so that as the input
signal increases land the traveling-wave tube 10 saturates
nearer the input end, the various couplers 40 to 43` still
additively combine to provide an increased -total signal.
This increase in dynamic range is 'at the expense of small
quently, like time portions of the input wave are recom
bined additively, so that the traveling wave in the adder 50
signal gain, but the gain can still be kept substantially
helix 26 is built up in a nonlinear fashion. The action
high. Additionally, the availability of the Vlinear output
of the third and fourth couplers 41, ‘t2 in contributing in~
makes
possible ‘great flexibility.
phase components to the traveling wave in the adder helix
The features of operation of this arrangement include
26 which correspond to like input portions of the signal
being amplified in the principal helix 16 is the same as 55 two considerations which make possible the desired re
sponse characteristic. First, in the operation of the com
that previously described.
bination it has been found that when saturation is reached
The net result, as seen -at the output of the adder hel-ix
in one of the coupling units 40 to 43, the response does
26, is ‘that a traveling wave -is built up which has much
not thereafter rem-ain constant for that coupler but, in
smaller amplitude variations than the variations fof the
stead,
decreases. Arrangements which rely Áon a con
input signal, and which result corresponds to the desired 60
stant maximum output from the individual stages to
increase in dynamic range. Substantially all of this non
achieve signal -'addition are therefore not applicable. In
linearly amplified energy is extracted by the output cou
stead,
in the present arrangement, the coupling of the
pler 3G and such as remain-s is dissipated in the resistive
first couplers (with respect to the traveling wave) is made
termination 29, in order to avoid reflective effects. The
to compensate for decreases in the output `of succeeding
synthesized output circuit 35 thus receives »the signals of
couplers, as the input signal increases. Consequently,
the desired response characteristic. The linear output
for
a preferred response there is a selected relationship
circuit 317 concurrently receives the regular output of «the
between the sequentially disposed couplers 40' -to 43
tube 10.
which is arranged to compensate for the operation `of
Thus this arrangement operates as an RF to RF arn
plifier, of increased dynamic range, and makes possible 70
the combination of -a number of functions in many cir
cuits. The 'traveling-wave helices employed are nondis
persive, and thus `the phase velocities of the signals along
the helices are independent of frequency in the frequency
«the `other couplers.
A »typical response for such an arrangement is shown
in FIG. 4, which represents the variation in output power
in milliwatts for variations in input signal. Only three
couplers were employed. The output power in milliwatts
is seen to be a substantially linear function of the input
range of operation. Thus the manner in which the sig 75 power in decibels relative to a milliwatt (dbm). The
response is therefore _essentially logarithmic. It can also`
n.211 analisti fram .the “Wehner/svelata@ 1_@ E may be
be seen thatthe normal saturation level of the »tube has
considered 'that the energy from the couplers is recom
been extended considerablyA by the mod-ilications made
bined in éa‘scaded series fashion to provide a summed o_ut
inthe external circuitry 'of the tube.
put. The delay -lineY constants may be adjusted further toà
compensate Afor delays or adjustments in th;e___RE signal
_
_
Another significant feature is derived from the posi
«tion ofthe tir'st of ‘the couplers `4t) relative 'to the input
in the traveling-_wave tube _10, it being well known that
there is a slowing ofthe _electron stream in a traveling
wave tube due to the loss o_f energy encountered in transit
of the tube by the electron stream.
couplery 23. As «the input signal increases to a large mag
nitude, a pointv is reached at which the traveling-wave
tube 10 is near saturation at its input end, a fact which
The detected signals applied to Ithe delay line 70 are
thus video signals which are additively combined. Both
the proportion of 'the-_energy coupled and the amount of
coupler 23k, however, this arrangement PDOVîdes that there
the _resistance S3 >to ¿S7 employed determines the contri
isa direct coupling of energy between these elements at
b_utionl of the individual couplers 46 to dil to the delay
high input signal levels.Y Consequently, with _a further
line‘ì'tl. Because _these contributions are added together
increase in the' input signal, the output continues to in_
in the delay line 7d, they determine the characteristic re
c?e'aswe despite saturation -of the traveling-wave tube 1_0.
sponse'__of the system, and permit the synthesis of specific
There is> no fundamental limitation on »the'xinput power
desired responsesf The manner in which two separate
le'v'el of l:operation of the traveling-wave tube 10, there
responses may be synthesized is shown in FIGS. 6 and 7,
io'r‘è, except Yfor structural failures.v _
_
_It will b'e appreciated "by those skilled in the art that 20 respectively. The arrangement utilized employed a sig
nal generator having a 310€) mc. input signal modulated
the~ luse of a signal removal technique with a traveling
at lQOO c.p.s. As shown in FÍG. 6, the video output volt
wave îfor the purpose of synthesis of a desi-red response is
age from the delay line was measured and plotted against
not'coniined -to
example` shown.` The _traveling wave
would normally limit the output from the ‘amplifier sys
By positioning the lirst coupler 4t) close to the input
the. input power, power being a more commonly used unit
may berconsidered to constitute :a spatial distribution o_f
inputsignal because‘any given portion _of the input
25
in traveling-wave tube work than is input voltage. Be
cause the, logarithm of »the input power is a function of
the logarithm of the input voltage, a straight line on FiG.
6 Ithus indicates a logarithmic response. The individual
curves for each coupler in FlG. 6 show l.that the compo
netic coupling can be made to a traveling wave. _ Thus the
slow wave structuresl and the couplers need n_ot be helices, 30 nents from the Separate detectors. are additively combined
to synthesize the desired logarithmic characteristic. The
for example, but they can instead be of other forms, such
output contribution from each coupler 46 to l50 is shown
as folded waveguides and _energy excited probes. The
as 1 Ato 5 respectively. Note that each except the first
traveling Iwave device, similarly, need not be a traveling
falls oli after reaching a peak. The iirst provides a con
wave tube but can be a-traveling wave version oi a maser
' tinually increasing contribution at high levels, because of
or parametric amplijier.
Y
signals‘hifïts in space as ‘the traveling wave grows. Con
sérìuently, the signal extraction and recombination tech
nique may effectively be employed wherever electromag
the direct coupling to. th‘e input coupler 23.
Another arrangement _in accordance with the inven
rlihis arrangement thus is `also illustrative of the manner
in which »the saturation and characteristics of the various
sections may be adjusted -to provide :the desired uniiied
tion; referring now to FIG. 5, may utilize »the successive
detection principle `in conjunction with a delay line tov
provide an RE conversion to a video output. As shown
in FlG. 5, a‘traveling-wave tube iiiy (indicated generally)
may have an input coupler 23 coupled tol -a source of _RF
energy (not shown)„_wh_ich is to be converted to~ a video
output with a specified amplification characteristic. _The
traveling-.Wave tube 1Q includesa principal helix 16, an
electron gun 1_3, and a.V collector 14,». Eositioned along
the length o_f the traveling-wave Itube 10 are tive helical
couplersj Alti-5() similar to those described »above al
though‘any number of> couplers may be used consistent
withthe lengths ofv theV individual couple-rs and of the
traveling-wave `tube.
_
Each of the helical transmission :line couplers 46~50
thus formed is coupled to agsepa'rate tapÍ _71 to 75 respec
tively on- a delay line 7€) through a diderent individual
detector, such as a crystal'diode 77 ’to 81 respectively, and
a variable resistive element S3 to 87 respectively having
a movable tap 89 to V93Y respectively. The delay line 70,“
»is composed in the usual form of distributed capacitance
and inductance elements. Successive points along the de-V
lay line 7G constitute 'the taps 7l to 75 respectively which
are connected 4to lthe traveling-wave :tube lil; ln this ar
40
result. Except-for the output of the first coupler 46, the
outputs from the individual couplers 47 Áto 50 lirst increase
with increasing input power, ,then reach maximum values
and then begin to decrease. The position of each cou
pler 46 to 50v and its coupling eñiciency determines 4the
45 nature of the curve. The settings of the variable resistors
83l to `S7 determine the relative contribution from each
coupler. Thus the total response from selected points can
50
be combined by proper control of these variables to give
the desired logarithmic result.
The curve `for the lresponse of the lirst couplervin FIG.
6 also illustrates the freedom from limitations due to the
saturation of the tube. Because of the direct coupling be
tween the input coupler 2_3 and the íirst coupler 46, the
output continues to increase. Variation of the position
of the iirst coupler 46 with respect to the input coupler 2_3
can be utilized to provide control vof this effect. In an
arrangement*constructedÍ in accordancel with this inven
tion, the response curve of FIG. 6 is achieved by varying
only the settingsv nfl the variable resistors ’83 to 87. lAs
seen in :FIGL 6, this arrangement .provides 'less than a 0.4
rangement, controlfof the coupling from; the separate
decible variation from a logarithmic response over a
points along the traveling-wave tube 1b can be accom
plished by adjustment ofthe variable resistors 83 to 87 ,» ask
range of 55 decibels. Furthermore, the saturation level is
over 40 >decibels greater than that possible by using a con
ve?tiona-l single-output coupler traveling-wave tube.
The same arrangement may also be utilized to provide
welll as by controly of the coupling ratiosY through selection
of »the number of turns and the proximity of the turns 1n> 65
a limiter type of response. .As shown in HG. 7, the
the individual couplers `46V to Sil'to the principal helix/16`
settings of the variable resistors -SG- to S7 can be adjusted
of. the traveling-wave tube 10.
»
to"V provide a selected
response, With avsubstan
The delay :time of the delay line 70 is selected to cor
" tially ilat characteristic, at the «power level selected for
respond to :the axialV phase veloci-ty' of the traveling wave
limiting. As may lbe seen
FIG. 7, `the limiting action
inthe traveling-wave tube. The diodes 77 to 81 consti-'
is constant to Within 0_‘5 decibel over a 42 decibel dy
tute‘detector elements forthe' microwave energy, the suc-V
cessively'coupledßout signals beingz applied to the coupled
namic range.
Other techniques may also be utilized to provide the
taps 71 to ’7S-of the del-ay lineV 70. Therefore, the delay
Y successive extraction and recombinationot signals. Thus,
line 70, serves as an adding network for recombi'ning in
time coincidence the like time portions of the input sig 75 as shown in FIG. 8, a microwave system may be utilized
3,084,293
9
in which there is again RF to RF operation. 'A cascaded
series of couplers and a signal delay device are again
used in providing RF addition of signals in a fashion cor
responding to the arrangement of FIG. l. Control of the
10
shown, for simplicity, as similar to the arrangement of
FIG. v8. To provide IF operation, however, each of the
couplers 46 to 48 is coupled to a different mixer 168 to
1li) respectively. Each mixer `108 to i110 is also re
phase `and relative amplitudes of the energy is achieved Ul sponsive to signals from a controllable variable frequency
in this arrangement through the use of variable attenu
oscillator i112. iOutputs from the mixers i108 to llt? are
ators, -variable phase Shifters, and microwave junctions.
coupled to a signal recombination circuit M5, which term
For simplicity, only three couplers 46 to 48 have been
is intended to indicate generally one of the forms of ad
shown at successive points along the length of a traveling
ditive circuits previously illustrated.
wave tube 10. The iirst of these couplers 46 (taken with 10
Therefore, the arrangement of FiG. l0 operates by
respect to the traveling wave) provides energy through a
mixing the RF signals removed by the various couplers
first variable phase shifter `95 and a iirst variable attenu
46 to 48 with the signals from the variable frequency
ator 96 to one symmetrical input of a ñrst microwave T
oscillator `112. Each mixer 108 to 11i) thus provides
junction 97. The second coupler 47 extracts energy from
an IF output, and each of the IF outputs are additively
the traveling wave and `couples it through a second vari
combined in phase in the signal recombination circuit
able phase shifter 99 and a second attenuator i100 to one
1l15.
Thus are lIF signals synthesized to a desired re
symmetrical input of a second microwave T junction itil.
sponse and made suitable for application to the output
The remaining input of the second T junction i101 is
circuit 35.
coupled to the third coupler 43 through a third variable
Thus there has been described an improved microwave
attenuator 163. Outputs from the second T junction i101 20 amplifier system and method by which selected dynamic
are coupled to the remaining input arm of the Íirst T
responses can be obtained. In general, the use of this
junction 97, outputs from `the `first T junction 97 con
technique permits an appreciable increase in the dynamic
stituting outputs from the system Iand being directed to
range of existing devices. Whether utilized for loga
the output circuit 35.
rithmic amplification or for signal limiting, or for some
The elements which may be employed in this arrange 25 other particular response, there is available a signal
ment have been indicated only generally, but may be co
compression which can markedly increase the versatility
axial forms of microwave transmission devices. It will
of a system. Inaddition to providing, for example,
be understood that the elements indicated as phase Shifters
greatly increased dynamic range, such devices can be
are intended to represent generally those devices which
arranged to operate from microwave signals and to pro
provide a relative phase diiference, whether through con 30 vide RF, IF or video output. In addition it should be
trolled or actual differences in electrical line lengths.
noticed that the system of the invention does not affect
Similarly, the attenuators may be any yform of amplitude
the operating characteristics of the principal device. For
control or power splitting device, and »the microwave
example, with traveling-wave tubes, the desirable char
junctions maybe any form desired of energy combination
acteristics of low noise and broad bandwidth are re
device.
tained as well as maximum amplification, if desired at
‘With this `version of an RF to RF amplifier, selection of
the same time. Although thus providing functions which
the amount of signal extracted from each of the coupling
have heretofore been accomplished only with complex
regions along the traveling-wave tube 10 is controlled both
arrangements, systems in accordance with this invention
by the characteristics of the couplers 46 to 48 themselves
are simple to construct and inherently stable and reliable.
We claim:
and by the values at which the variable attenuators 96, 40
l. A microwave amplifier for providing, from an input
190, 193 are set. The variable phase Shifters 95, 99 are
adjusted to provide in-phase coupling of the microwaves
microwave signal, an output microwave signal of corre
from the iirst coupler 46, the second coupler 47 and the
sponding frequency and selected signal relation, said
Energy removed from the traveling
system comprising: a traveling-wave tube ampliiier having
wave in the tube if* at the second coupler 4'7 is delayed
suii‘iciently to be combined in phase `at >the second T junc
tion liti with energy extracted from the third coupler 48.
Thus like sivnal portions are recombined in time coinci
dence. A similar delay of the energy from the first
an extended helical slow-Wave structure defining a central
third coupler 48.
axis from an input end thereof, the helical slow-wave
structure having selected axial phase velocity character
istics; a second helical slow-wave structure proximate,
substantially parallel to and substantially coextensive with
coupler 46 is effected, to provide a further in-phase rela 50 the helical slow-wave structure of the traveling-wave
tube; an input circuit including an input helix wound
tionship, so that combination of the output of the second
concentrically about the input end of the helical slow
T junction lil-1 and the output of the iirst attenuator 96
wave structure for providing thereto a signal to be
gives the .final recombined signal output from the :first T
amplified; a number of energy intercoupling means for
junction 97 to the out-put circuit 3S. Thus this is another
the transfer of electromagnetic energy from the helical
form of RF to RF operation which may `be preferable in
some instances.
slow-wave structure to the second helical structure, each
of said energy intercoupling means including a different
The chart of output power in milliwatts versus input
helical coupler about the helical slow-wave structure of
power, FIG. 9, shows the manner in which a logarithmic
said traveling-wave tube for extracting energy from a
response may be provided with a desired synthesized
characteristic from the arrangement of FIG. 8. It may 60 region thereof and a helical coupler about a region of
the added helical structure for providing energy thereto,
again be seen that the signal from the first input coupler,
designated by curve lP1 increases sharply with high input
the spacings between the adjacent intercoupling elements
on the helical slow-wave structure and the corresponding
signals, because the arrangement is again such that a
elements on the additional helical structure being alike;
direct coupling exists between the input helix 23 and the
first coupler 46 at these signal levels. The signals re 65 and an output circuit including an electromagnetic en
ergy wave coupler coupled to the additional helical struc
moved by the remaining two couplers 47 and 48, how
ture in a region oppositely disposed from the input circuit
ever, drop oiî after reaching peaks, as is shown by curves
with respect to the energy intercoupling means.
P2 and P3. The ñnal synthesized response, shown by curve
2. A microwave amplifier comprising: a traveling-wave
Peut, is a desired logarithmic response. FIG. 9 also shows
some typical operating relationships for the traveling 70 tube having a gun end and a collector end and a helical
slow-wave structure disposed along the electron stream
wave tube.
therebetween, the electron gun end being the input end of.
The device in accordance with the invention may also
the tube, the tube also including an envelope substantially
be `utilized »to provide RF to IF conversion of signals.
pervious to microwave energy and contiguously en
Such an arrangement is illustrated in FIG. l0, in which
the arrangement of couplers 46 to 48 on a tube l0 are 75 compassing the helix; a layer of resistive material dis
aos/4,293
1
Il,
,
-
1
Y
posed o‘n‘ they outer surface ofthe envelopeY for providing
the adder helix for extractin;D (therefrom the‘fully re!
com'bine'd signals;l and outp‘t'ftAïn'i'ea'nsI for linear signals
uniformity ofV the traveling Wave and lr'riinirnizifng reliée
tio'ns in the tube; an adder- helix disposed adjacentand
including a coupler at the-output end of the traveling
substantially parallel the
Wave tube helix.
o’f Athe traveling-wave tube,
i
‘t
d
_
`
3. A system for amplit'yi g' electromagnetic Wave
the adder helix being aoleas't’partially coexten'sive with'
the helix of the traveling-wave tube land having like
energyr comprising in combination‘í electron gun _means
for launchinga stream of electrons’- along a predeterê
mined path, of1 lixed zlength, a ii'rst s_low-Wayestructujre
disposed ¿16mg and ¿666i said pata" for' pr‘dpagafifigfeiee
tromagné'tic vvave energy in such manner as to4 provide
electrical characteristics as to the propagation of a
traveling wave, the input and output ends of the adder
helix corresponding to the like ends" of the'- travelinglvvave'"
tube; a resistive termination coupled to the adder >helix 10
at the output end thereof; a source of input signals to be'
interaction lhetvveeri saidy electron stream and said elec
tromagnetic Wave energy, input «coupling means disposed
amplified; an input coupler of helical form encompassing
adjacent theeríd-> of saidV lfirst' slovv-vvave Structure near
the envelope of the traveling-wave’ tube at the input end
of the helix therein and being concentric with the helix,
the input coupler launching the traveling wave onto the
traveling-Wave tubev helix; a group of microvvaveenergy
couplers, each consisting of a helical coupler en
compassing a region> of the traveling-wave tube 'envelope'
and a helical coupler coupled thereto encompassing a
«estl said electron gun means for launching an electro
magnetic vvave onto said first slow-Wave structure, where
by said electromagnetic wave- travels along said ñrst slow
wave structure, a second slow-wave structure having
[substantially the Vsame* electromagnetic wave propagating
characteristics as said iirst slow-wave structure disposed
"substantially _parallel to and coextensive with said ñrst
portion of the adder helix, each ot the couplerhelices
on the traveling-waver tube providing extraction of electro-Y
slow-Wave structure, and a plurality of signal transfer
magnetic wave energy from the traveling-'Wave tube helix
and each of the couple'dphelices on the adder helixf launch
ing the energy onto the adder helix, the spacings be
tween adjacent successive coupling helices on the travel
ing-wave tube and the _corresponding coupling helices
along the length of the adder helix being alike, each of
the couplers thus providing extraction ‘of the same input
signals'` at selected time delays,> the adder helix providing
means
coupled tofsarid first and second slow-WaveV struc
tures at spaced regions along the vlengths thereof for
_successively -removing- selected portions of the electro
" magnetic wave traveling along said ñrst slow-wave struc
ture and'launching .the removed portions of said wave
ont-o said second slow-Wave structure in time coincidence
relative to said wave traveling along said first slow-Wave
structure.
complementary time delays as to signals which: are 30
launched thereon so that the signal contributions from
the energy couplers return toA time coincidence at'y a
References Cited in the ñle of this patent
UNITED STATES PATENTS
selected total delay atI the last coupler'on the adder helix,
2,726,291
a response characteristic for the system being selected
2,733,305
by choice of the relative axial positions of the couplers 36 2,804,511
Diemer ______________ __ lan. 31, i956
2,981,889
Webber _____________ __ Apr, 25, 1961
706,094
Great Britain _________ __ Mar. 24, 1954
and the coupling eñ‘iciency of _the couplers, the couplersy
being arranged to compensate for nonlinearity after satu
ouate ____________ __'___-_ Dec. 6, 1955
Kompfner __-_____-___~___ Aug; 27, 1957
ration in the couplers adjacent the output ends of the
two helices; output rmeans for synthesized signals in
cluding an output helix encompassing theoutputend, of
40
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